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    THẠC SĨ Acoustic communication in Australian fur seals

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  6. Acoustic communication in Australian fur seals


    Communication is a fundamental process that allows animals to effectively transfer information between groups or individuals. Recognition plays an essential role in permitting animals to distinguish individuals based upon both communicatory and non-communicatory signals allowing animals to direct suitable behaviours towards them. Several modes of recognition exist and in colonial breeding animals which congregate in large numbers, acoustic signalling is thought to be the most effective as it suffers less from environmental degradation.

    Otariid seals (fur seals and sea lions) are generally colonial breeding species which congregate at high densities on offshore islands. In contrast to the other Arctocephaline species, the Australian fur seal, Arctocephalus pusillus doriferus, along with its conspecific, the Cape fur seal, A. p. pusillus, display many of the behavioural traits of sea lions. This may have important consequences in terms of its social structure and evolution. The acoustic communication of Australian fur seals was studied on Kanowna Island, Bass Strait, Australia. Analysing the acoustic structure of vocalisations and their use facilitates our understanding of the social function of calls in animal communication. The vocal repertoires of males, females, pups and yearlings were characterised and their behavioural context examined.

    Call structural variations in males were evident with changes in behavioural context, indicating parallel changes in the emotive state of sender. For a call to be used in vocal recognition it must display stereotypy within callers and variation between them. In Australian fur seal females and pups, individuals were found to have unique calls. Mutual mother-pup recognition has been suggested for otariids and this study supports the potential for this process to occur through the use of vocalisations. Call structural changes in pup vocalisations were also investigated over the progression of the year, from birth to weaning. Vocalisations produced by pups increased in duration, lowered in both the number of parts per call and the harmonic band containing the maximum frequency as they became older, suggesting calls are changing constantly as pups grow toward maturity. It has been suggested through descriptive reports, that the bark call produced by males is important to vocal recognition.

    The present study quantified this through the analysis of vocalisations produced by male Australian fur seals. Results support descriptive evidence suggesting that male barks can be used to discriminate callers. Traditional playback studies further confirmed that territorial male Australian fur seals respond significantly more to the calls of strangers than to those of neighbours, supporting male vocal recognition. This study modified call features of the bark to determine the importance to vocal recognition. The results indicate that the whole frequency spectrum was important to recognition.

    There was also an increase in response from males when they heard more bark units, indicating the importance of repetition by a caller. Recognition occurred when males heard between 25-75% of each bark unit, indicating that the whole duration of each bark unit is not necessary for recognition to occur. This may have particular advantages for communication in acoustically complex breeding environments, where parts of calls may be degraded by the environment. The present study examined the life history characteristics of otariids to determine the factors likely to influence and shape its vocal behaviour. Preliminary results indicate that female density, body size and the breeding environment all influence the vocal behaviour of otariids, while duration of lactation and the degree of polygyny do not appear to be influential. Understanding these interactions may help elucidate how vocal recognition and communication have evolved in different pinniped species.




    CHAPTER 1. General Introduction

    1.1 Communication and vocal recognition

    1.2 Otariid pinnipeds

    1.3 Australian fur seals

    1.4 Overall aims and structure of the study

    CHAPTER 2. Characterisation of Australian fur seal vocalisations

    2.1 Introduction

    2.2 Materials and Methods

    2.3 Results
    2.3.1 Affiliative calls
    2.3.2 Aggressive vocalisations
    2.3.3 Dual function call

    2.3.4 Behavioural context of the bark call

    2.4 Discussion
    CHAPTER 3. Individual variation in the pup attraction call produced by

    female Australian fur seals during early lactation
    3.1 Introduction

    3.2 Materials and Methods

    3.2.1 Study species

    3.2.2 Data collection and acoustic analyses

    3.2.3 Description of the Pup Attraction Call

    3.2.4 Statistical analysis of the Pup Attraction Call

    3.2.5 Peak frequency distribution in the Pup Attraction

    3.3 Results

    3.3.1 Description of the Pup Attraction Call

    3.3.2 Inter-individual variation

    3.3.3 Classification of variables

    3.3.4 Peak frequency distribution in the Pup Attraction

    3.4 Discussion
    CHAPTER 4. Changes in call structure of Australian fur seal pups

    throughout the maternal dependency period

    4.1 Introduction

    4.2 Materials and Methods

    4.2.1 Data collection and acoustic analyses

    4.2.2 Statistical analysis of the Female Attraction Call

    4.2.3 Call structure changes with age

    4.3 Results
    4.3.1 Potential for Individual Coding

    4.3.2 Discriminant Function Analysis

    4.3.3 Classification And Regression Tree analysis

    4.3.4 Call structure changes with age

    4.4 Discussion

    CHAPTER 5. Species-specific characteristics and individual variation

    of the bark call produced by male Australian fur seals, Arctocephalus

    pusillus doriferus

    5.1 Introduction

    5.2 Materials and Methods
    5.2.1 Data Collection

    5.2.2 Definitions

    5.2.3 Acoustic Analysis

    5.2.4 Characterisation of the bark call
    5.2.5 Statistical analyses

    5.3 Results

    5.3.1 Characterisation of the bark call

    5.3.2 Intra- versus inter- individual variation

    5.3.3 Inter-individual variation
    5.4 Discussion

    CHAPTER 6. Who goes there? The dear-enemy effect in male

    Australian fur seals (Arctocephalus pusillus doriferus

    6.1 Introduction
    6.2 Materials and Methods

    6.2.1 Study site and recording methods

    6.2.2 Design of playback experiments

    6.2.3 Criteria of Response
    6.3 Results

    6.4 Discussion

    CHAPTER 7. General Discussion

    7.1 Functionality of calls

    7.2 Factors influencing the acoustic behaviour of Otariids

    7.3 Are Australian fur seals vocalisations more like sea lions

    7.3 Future research


    Acoustic communication in Australian fur seals(Tạm dịch:Acoustic truyền thông trong hải cẩu Úc)

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